The present invention relates to a bearing device for use in a rotary macine such as a turbocharger which is satisfactorily capable of absorbing and damping vibrations and which ensures satisfactory lubrication so that a service life of the bearing device can be increased.
Conventional oil film dampers used in small-sized turbochargers having ball bearings may be divided into a complete float supporting type and a semi-float supporting type. In the complete float supporting type bearing device, an oil film damper is supported only by an oil film and its movement is not restricted. In the semi-float supporting type bearing devices, a retaining pin or the like is fixed to one end of the oil film damper or one end of the oil film damper has a flange so as to prevent the rotation of an oil film damper.
FIG. 1 shows, for instance, a bearing device which is used in a small-sized turbocharger and has a semi-float supporting type oil film damper. Reference numeral 31 designates a bearing housing; 32, a portion of the housing 31; 33, a turbine shaft; 34, a ball bearing on the side of a turbine; 35, a ball bearing on the side of a compressor; 36, a bearing spacer; 37, a preloaded spring; 38, an oil film damper; 39, a retaining pin for preventing the oil film damper 38 from rotating; 40, a damper retainer; 41, an oil thrower spacer; 42, an oil thrower; 43, an oil inlet; 44, an oil outlet.
In the bearing device for the turbocharger of the type as shown in FIG. 1, the oil film damper 38 and turbine shaft 33 are lifted by the pressure of the lubricant fed to an oil film formed between the inner surface of the bearing housing portion 32 and the outer peripheral surface of the oil film damper 38. The load-carrying oil film is capable of damping vibrations transmitted from turbine shaft 33. The above-described capabilities are attained because the turbocharger is small in size.
Since the turbocharger is small in size, the bearing device of the type as shown in FIG. 1 presents no problem; but when the rotary machines become large in size and the weight of a rotating shaft is increased, enlargement by only scaling up the oil film damper 38 of the type as shown in FIG. 1 is not enough to lift up the turbine shaft 33 unless the lubricant under a considerable pressure is fed to the load-carrying oil film. The increase in pressure of the lubricant results in the increase in quantity of lubricant to be fed to the turbocharger. As a result, there arise the problems that end leakage is increased and that the mechanical efficiency is decreased. In addition, there arises the problem that carbon bridges are produced due to the high temperature of the turbine.
With the ball bearings as shown in FIG. 1, the DN value is extremely higher than a million so that it is essential to form a complete oil film on the bearing surface in order to ensure the service life of the bearings. However, the ball bearings 34 and 35 are mounted in the oil film damper 38 so that it becomes difficult to directly lubricate them from the exterior and consequently part of the oil film formed around the outer cylindrical surface of the oil film damper 38 is used to lubricate the ball bearings 34 and 35. For instance, as shown in FIG. 2, the so-called jet system may be employed in which a lubrication hole 45 is drilled through the oil film damper 38 such that the lubricating oil is fed to the ball bearing 34 in the direction indicated by the arrow. Furthermore, as shown in FIG. 3, the so-called splash lubrication system may be employed in which the lubricating oil which flows out of an end of the oil film damper 38 is caused to impinge on the oil thrower spacer 41 carried by the turbine shaft 33 as indicated by the arrows so that the lubricating oil is atomized, thus forming an atmosphere of lubricating oil mist.
However, when the operating conditions become severe, the lubricating systems as shown in FIGS. 2 and 3 cannot satisfactorily lubricate the ball bearings 34 and 35. Especially when the ball bearings are provided with a cage or a preloaded spring 37 is disposed in the oil film damper 38, there arises the problem that the jet of the lubricating oil is interrupted and the ball bearings are not satisfactorily lubricated.
The present invention was made to substantially overcome the above and other problems encountered in the conventional bearing devices for rotary machines. More particularly, in a bearing device for a rotary machine of the type having an oil damper fitted over ball bearings, the present invention is characterized in that the oil film damper is of a semi-float type in which the oil film damper is supported at one portion thereof and the ends of the oil film damper are maintained free and a plurality of beam-like arms interconnect between the supported portion of the oil film damper and the oil film formation portion at each end of the oil film damper, thereby providing a Rahmen or rigid frame structure. In addition, the bearing device in accordance with the present invention is characterized in that satisfactory lubrication can be accomplished within a limited narrow space so that the service life of ball bearings can be increased.
Therefore, even in the case of a large-sized rotary machine having a heavy rotating shaft, a portion of the oil film damper is inherently supported by the bearing housing and the ends of the oil film damper are maintained free so that the formation of the oil films at those portions at the ends of the oil film damper is facilitated. As a result, the bearing device of the present invention can satisfactorily absorb and damp vibrations at a minimum feeding pressure of lubricating oil. In addition, the structure between the supported portion and the oil film formation portion is a Rahmen or rigid frame structure comprising a plurality of beam-like arms so that the oil film damper has a suitable degree of rigidity. Moreover, a space between the adjacent arms provides an oil passage so that the lubricating oil can be easily discharged. Furthermore, the manufacturing of the oil film damper in accordance with the present invention is easy because a plurality of arms can be defined when a plurality of slots are cut through the cylindrical surface of the oil film damper.
According to the present invention, the ball bearings mounted in the oil film damper are not lubricated alone with part of the oil film formed over the outer surface of the oil film damper as in the conventional bearing devices, but are lubricated directly by a high velocity jet of lubricating oil fed from the exterior of the oil film damper. As a result, the lubrication of the ball bearings is positively ensured.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of a preferred embodiment thereof taken in conjunction with the accompanying drawings.